The present invention relates to a novel solid state thermal process for the preparation of lithium cobaltate (LiCoO2) useful as a cathode material in nonaqueous, solid state and polymer electrolyte for secondary rock in chair or intercalated batteries.
Lithium cobaltate (LiCoO2) is widely used as a cathode in lithium secondary cells in the view of its high reversibility to lithium ions and less fading capacity over LiNiO2 and LiMn2O4 electrodes.
Methods reported in the art for the preparation of cathode lithium cobaltate (LiCoO2) disclose the reaction of lithium nitrate, or lithium hydroxide, lithium acetate or any other lithium salts with cobalt nitrates, oxides, acetates, hydroxides, sulphates by soft chemistry method like sol-gel process between temperature ranges of 350-500xc2x0 C. for long duration of time and multistep preparation procedures. Normally, in solid state thermal methods in the synthesis of these oxide materials, the duration of preparation is long heating, intermittent cooling and grinding process. Other preparation methods are also available in literature for synthesizing lithium cobaltate like pulsed laser deposition, sputtering and electrostatic spray deposition.
1. xe2x80x9cSynthesis and electrochemical properties of LiCoO2 spinel cathodesxe2x80x9dxe2x80x94S. Chol and A. Manthiram, Journal of the Electrochemical Society, Vol. 149(2) (2002) A162-166.
2. xe2x80x9cX-ray absorption spectroscopic study of LiAlyCO1-yO2 cathode for lithium rechargeable batteriesxe2x80x9dxe2x80x94Won-Sub Yoon, Kyung-Keun Lee and Kwang-Bum Kim, Journal of the Electrochemical society, Vol. 149(?) (2002) A146-151.
3. xe2x80x9cHigh temperature combustion synthesis and electrochemical characterization of LiNiO2, LiCoO2 and LiMn2O4 for lithium ion secondary batteriesxe2x80x9dxe2x80x94M. M. Rao, C. Liebenow, M. Jayalakshmi, M. Wulff, U. Guth and F. Scholz, J. of Solid State Electrochemistry, Vol. 5, Issue 5 (2001) 348-354.
4. xe2x80x9cFabrication of LiCoO2 thin films by sol gel method and characterization as positive electrodes for Li/LiCoO2 cellsxe2x80x9dxe2x80x94M. N. Kim, H. Chung, Y. Park, J. Kim, J. Son, K. Park and H. Kim, Journal of Power Sources, Vol. 99(2001) 34-40.
5. xe2x80x9cPreparation and characterization of high-density sperical LiNi0.8CoO2 cathode material for lithium secondary batteriesxe2x80x9dxe2x80x94Jierong Ying, Chunrong Wan, Changyin Jiang and Yangxing Li, J. of Power Sources, Vol. 99 (2001) 78-84.
6. xe2x80x9cElectrochemical characterization of layered LiCoO2 films prepared by electrostatic depositionxe2x80x9d, Won-Sub Yoon, Sung-Ho Ban, Kyung-Keun Lee, Kwang-Bum Kim, Min Dyu Kim and Jay Min Lee, J. of Power Sources, Vol. 97-98 (2001) 282-286.
7. xe2x80x9cEmulsion-derived lithium manganese oxide powder for positive electrodes in lithium ion batteriesxe2x80x9d Chung-Hsin Lu and Shang-Wei Lin. J. of Power Sources, Vol. 93(2001) 14-19.
8. xe2x80x9cCobalt doped chromium oxides as cathode materials for secondary batteries for secondary lithium batteriesxe2x80x9d Dong Zhang, Branko N. Popov, Yury M. Poddrahansky, Pankaj Arora and Ralph E. White, J. of Power Sources, Vol. 83 (1999) 121-127.
9. xe2x80x9cSynthesis and electrochemical studies of spinel phase LiMn2O4 cathode materials prepared by the pechini processxe2x80x9d W. Liu, G. C. Farrington, F. Chaput and B. Dunn, Journal of the Electrochemical society, Vol. 143, No.3(1996) 879-884.
The above reported conventional processes show several disadvantages. Generally any one or all of the following are seen:
1. Side reactions occur, i.e., formation of unexpected and unwanted byproducts.
2. Unreacted material is left behind which acts as impurity.
3. Partial reactions occur.
4. Several steps and long calcination time are needed for preparation.
5. Controlled conditions required.
6. Undesirable phases formed.
It is therefore important to develop processes which overcome the disadvantages enumerated above.
The main object of this present invention is to provide a novel method for the preparation of Lithium cobaltate (LiCoO2) hitherto unattempted which obviates the drawbacks mentioned above.
It is another object of the invention to avoid multi-step processes, formation of undesirable and unexpected byproducts and undesirable phases reported in prior art.
These and other objects of the invention are achieved by the novel process of the invention comprising solid state thermal one step reaction of lithium oxide and cobalt nitrate
Accordingly, the present invention relates to a process for the preparation of lithium cobaltate by a solid state thermal one step process comprising mixing lithium oxide (Li2O) and cobalt nitrate (Co(NO3)2) in solid state uniformly, adding a heat generating material to the mixture and grinding the mixture, heating the ground mixture at a temperature in the range of 650 to 700xc2x0 C. to obtain the desired lithium cobaltate.
In one embodiment of the invention, the ratio of the Li2O+Co(NO3)2 mixture and the heat generating material is 1:3.
In another embodiment of the invention the ground mixture is heated in a furnace for about 8 hours.
In one embodiment of the invention, the Li2O is mixed with Co(NO3)2 in the following ratios.
Li2O:Ni(NO3)21:2 
In another embodiment of the invention, the heat generating material is selected from urea and ammonium nitrate.
In yet another embodiment of the invention electric furnace is used for heating.
In still another embodiment of the invention, the materials used are all in solid state.